An air-conditioning apparatus such as a building multi-air-conditioning apparatus has a configuration in which an outdoor unit (heat source unit) placed, for example, outside a building and an indoor unit placed in the building are connected through a refrigerant pipe. By causing refrigerant circulating in a refrigerant circuit to transfer or receive heat to or from air, the air-conditioning apparatus heats or cools an air-conditioned space. At a compressor of the air-conditioning apparatus, when a discharge temperature increases, a temperature of a refrigerating machine oil or sealant may exceed a guaranteed temperature. To solve this problem, a measure is necessary to decrease the discharge temperature of the compressor.
An air-conditioning apparatus equipped with an injection circuit is described in Patent Literature 1. The injection circuit of the air-conditioning apparatus has a configuration in which a bypassing expansion device, the refrigerant heat exchanger, a first on-off valve, and a compressor injection port are connected in sequence via an injection pipe branching off from a refrigerant pipe of a main circuit at a point between a refrigerant heat exchanger and a load side expansion device. In the compressor, the refrigerant sucked through the main circuit is compressed to an intermediate-pressure refrigerant, and is then merged with refrigerant injected from the injection circuit. The merged refrigerant is compressed to a high-pressure refrigerant and then is discharged.
Also, a scroll compressor equipped with an injection pipe is described in Patent Literature 2. In the scroll compressor, an outer end of a fixed scroll lap and an outer end of a movable scroll lap are installed close to each other. An intake port configured to introduce refrigerant gas to a compression chamber is formed on each of an external surface side and an internal surface side of the outer end of the movable scroll lap. A pocket is formed in the vicinity of the intake ports by a partition portion. An injection pipe is laid under the pocket to release oil or liquid refrigerant to the pocket.